I have put an 11-30 on a short cage Shimano mech with no issues.
Also have a medium cage running a SRAM 11-36 cassette on a Shimano mech with a reversed B-screw. No others mods and changes gear as well as it ever did.
The length of cage lets The mech take up slack in chain so main consideration is differential between the longest the chain has to be (big big) and shortest (small small).
If you have a wide spread on rear like 11-32 and a big gap like 50-34 front then you hit limit of short cage if you use every gear combo (namely big big)
If you have something like 46-36 up front it makes things easier, hence going way over rear cassette size on my CX bike (the 11-36) with no issues.
Likewise if you do not cross the chain to extremes you can get away with a shorter chain length than you might otherwise need and again may be able to use a shorter cage mech