Hello Eric,
Here, I have a similar configuration with a single RF interface and APRX transmit from APRS-IS on RF messages to others SSID with the same call.
I do not remember if I have modified the original "aprx.conf" config file but I have positive filters in "source" sub-sections of "digipeater" section.
Extract of my config file is below.
You can note I have added a negative filter to reject packets without interest to leave space in our VHF 1200 bds channel.
Hope that can help you :)
73 de F4ACU
Matthieu
<digipeater>
transmitter $mycall
ratelimit 60 120
srcratelimit 10 20
<source>
source $mycall
relay-type digipeated
filter -t/coistunw # block cwop, objects, items, status, telemetry, User-defined, NWS format messages and objects and Weather
filter t/pmq # digipeat positions, messages and queries only
<wide>
keys WIDE,FR
maxreq 3
maxdone 3
</wide>
</source>
<source>
source APRSIS
relay-type third-party
via-path WIDE2-2
msg-path WIDE2-2
#viscous-delay 5
filter -t/coistunw # block cwop, objects, items, status, telemetry, User-defined, NWS format messages and objects and Weather
filter t/pmq # transmit on RF positions, messages and queries only
</source>
</digipeater>