Also after 2/1 you have to accommodate 18-21 range without going beyond 4M too often.
In polish club you have two ranges so all "reverse" bids after 2/1 are 15-17 in standard:
1S - 2C
???
Let's say you have strong one suited hand in spades here. If you jump there will be no way for responder to show his range and allow space for cuebids (because if he bids 4S with minimum you may still have 18-21 and if he bids 4D/4H cuebid every time then you don't know his range if you are in 15-17). If you bid conventional 2S (any one suited or something) then you need artifical follow ups to differ between 11-14, 15-17, 18+. Those things are done in serious 2/1 systems but people playing "vanilla" runs into trouble all the time, especially with popular but imo very weak style of raising 2/1 without extras:
1S - 2D
3D = should be extras or you are completely screwed at 3 level and responder still in 11-21 range.
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by faking reverses and the like.
This is btw pretty amazing. The way to solve this is to either play "multireverse" (reverse = any 16+) or conventional 2NT (which only works in polish/dutch club style). This is necessary in 2/1 even more so than:
1C - 1M
2D
relay in polish club which you can easily live without and which is much simpler to learn (you just respond by steps how many M card you have and what range). However somehow you always hear that in pc you need to learn artificial stuff while much more complicated convention absolutely needed in sane 2/1 is played by feel (let's fake a reverse here or jump there without any clear rules).