The flame/exhaust animation of SRB-U nozzles and (to a lesser extent) the SRB-A-G nozzle starts too far up/clips the nozzle. All SRB-U-nozzles are affected. (I use realplume)
I'm not sure about how the SRB-A-G nozzle can be handled, that would probably need 4 separate fire/exhaust animations to look perfect.

Interesting, will see what I can do about it. No guarantees though as the stock effects are... limited... as to what can be adjusted (is why RealPlumes is highly recommended; those I can actually adjust/rescale/etc).

The SRB-U config was copied/cloned from the SRB-A, so in theory, they should use the exact same effects setup (size, position, etc).

Though if it is a transform positioning error, then it probably effects the realplume setup as well.

I do use realplume. :)

Even more interesting -- the RP patch for the SRB-A might be broken then, as that looks like the stock effects on both the -A and -U models.

If you zoom out in the screenshot posted above with both -A and -U nozzles, are there different plumes used between the two?

(already known that the SRB-U lacks RealPlume configs, which might explain part of why the effects look so off)

One change / addition that I could make, that would help with both stock and RP effects, is to add a per-nozzle-model config setting for 'position' -- so that the effects might be positioned correctly even for 'long' nozzles

Fixed up the real-plume effects -- was some additional problems with patches as RealPlume was not removing the existing effects properly (as the part also includes ModuleRCSFX).

Seems like the SRB-As use realplume while the SRB-Us don't?

Thanks for the confirmation :)

Yeah, looks like the majority of this issue is simply that the SRB-U parts don't have RealPlume configs yet (already fixed in dev).

the stock effects... still not much I can do about those, but I'll take a stab at it this evening if I have time (might be able to adjust the position a bit... but they still lack any sort of scale control).