Namaste Sri Darshat Shah,
Thank you for your interest and response. I've seen the pages relating to Magadha in BC Law's book that you have kindly provided a link for - and I don't see anything much of relevance in terms of arguments about Magadha's location or about the possibility of Greater Magadha - I will study the book more carefully and comprehensively to see if it offers any new perspectives beyond simply claiming that Magadha lies to the east or that Vairantya lies near Mathura.
Regarding your specific points:
1. I have already shown (with a map) how Śrāvastī can be accurately described as being a far-northern city compared to Girivraja (if we take Girnar as Girivraja and Śrāvasti as the town popularly associated with Lava (i.e. Lahore) - or some such prominent place in northern Punjab.
The UP Kosala is not north of Bihari Magadha, it is right adjacent to it, and the UP Śrāvasti is more west than it is north of Rajgir. Besides that, as I said, there is nothing excavated in Patna and Rajgir (or even the UP Shravasti) that more securely and conclusively connects Magadhans, Mauryans, Girivraja & Pāṭaliputra than the direct words of Aśoka at Girnar, and the words (at the same location) of Rudradāman-I a few centuries later connecting Girnar to the administrative work of Chandragupta Maurya as well. Clearly therefore Girnar was a well known place known to (and being the site of activity of) several generations of Mauryan and post-Mauryan rulers. But here is a map of Rajgir/Patna to Shravasti which shows more of a west-east than a north-south relation between UP Kosala & Bihari Magadha (and the cities as well)

2. Buddhist reliquary sites are not concentrated to the same extent in UP & Bihar as they are in the North-Western region (or even the Gujarat, Western-Maharashtra, Sindh region). For example, we already know of Sanchi, Bharhut etc in Central India (although these are not located in the UP & Bihar regions associated with Kosala and Magadha). The Punjab region on the other hand (both east and West) has so many early excavated Buddhist sites. In and around Takshashila alone, I've identified about 20 sites connected to early-Buddhism, many of them stupas, as shown by the blue pins on the map below.

We cannot use stupas alone as conclusive evidence, as there are stupas even in Sri Lanka, Myanmar, Thailand etc - but have to consider their earliness and concentration at a single site to decide what the site meant to early Buddhism (along with other evidence).
3. No - Verañja (Vairantya in Sanskrit) is described as being right next to uttarakuru in the North-western India in the Pali canon - please read the links I posted earlier. In one of the suttas whose links I posted earlier, of the Buddha's prominent Brahmin disciples known only by his gotra name Maudgalyāyana (Moggallāna), suggests to the Buddha that since Verañja was facing a famine at that time, and most of the monks could find no one to spare them alms of food, that they all cross over to neighbouring uttarakuru for alms. The Buddha tells him to drop the idea of visiting uttarakuru for begging. Uttarakuru was located nowhere near Mathura, so if BC Law opines that Verañja was near Mathura, I wonder what evidence he offers. I searched the books you mentioned at
archive.org but couldn't find anything in them about Verañja. However
this article mentions something about the NW-location of Verañja in the Pali canon but it is using the same reference as I have mentioned above.
I did not claim that
Verañja was closer to Girnar, I said it would have been close to Śrāvasti as the Pali canon talks of common people from Verañja visiting Śrāvasti, so since Verañja is located next to Uttarakuru, it is in the extreme North-west - and Śrāvasti must have also been somewhere that is not too far from Verañja.
4. Śrāvasti is not recorded as being close to Rājagṛha anywhere that I have seen. Magadha and Avanti are in/near Dakṣiṇapātha, while Kāśi/Kośala/Videha which are closer to the Śibis/Uśinaras etc are closer to Uttarapātha (both with respect to Āryāvarta/Madhyadeśa whose southern boundary was the pāriyātra/vindhya range).
5. Let me draw your attention to Major Rock Edict of Ashoka 1 - his very first order in his very first edict is to ban animal slaughter in his kingdom (idha na kiṃci jīvaṃ...) and commit himself to vegetarianism - and the grammarian Kātyāyana in his vārttikas refers to devānāṃpriya (the title of the Mauryan kings) as an exception to Pāṇini's sūtra 6.3.21 and mentions of him as the vegetarian king (śāka-pārthiva) while commenting on sūtra 2.1.69. We have to see where Aśoka's ban had the most effect - in Magadha itself surely? Do you think Bihar (or the eastern janapadas) became predominantly vegetarian - or does vegetarianism fit the description of Gujarat/Rajasthan etc? Here is a map which makes the answer easy.
As you can see from the arguments I am making, knowing the facts and being able to connect them with logic are two different things. Many scholars know a lot of facts, all the facts are already out there in the public domain. It's how we connect them together that makes all the difference.
I hope to present other arguments in support of my facts if the need arises. Greater Magadha is not a terribly intelligent proposition I am afraid.
Thanks,
Ramakrishnan Suryanarayanan