Cbet sizes differences between 3bet pots and single raised pots

Well 3bet pots have smaller cbets in general, part of that being that 3bet pot at 50bb has much lower SPR than SRP pot at 50bb deep. But there are more things to consider. The largest or smallest sizings are often happening on completely different flops in SRP vs 3bet pots. Big reason for why we don't use many huge cbets OOP in SRP is that flatter range will be very pocket pair heavy, so very often flatter flops a set more often than the opener. Which is a big problem, especially deeper stacked.

Overall I recommend trying to go more in detail, look at some aggregate reports for specific spots and see what is the approach there. This "bigger IP in SRP and bigger OOP in 3b pots" approach is way too broad.

Also there is very significant difference in how you should play vs BB compared to vs SB. Even if both are IP SRP.

In general, we are more inclined to bet marginal hands when out of position. Eg with KK on an A-high board, checking is quite nice in position, since we close the action and get to see the turn for free. But out of position it becomes more reasonable to bet, otherwise IP can just bet his Ax and check behind the smaller pairs that we beat - not a great result. It’s this tendency to bet marginal hands that leads to smaller sizes when OOP.

In 3bp it’s a bit different because the SPR is much lower. If IP cbets too large, OOP can just start checkraising a ton of 1p hands for protection. This makes it necessary for IP to size down.

OOP call vs 3bet is also very pocket pair heavy, and there are a ton of high boards where these pairs are just trash. Betting big as the 3bettor makes no sense because the caller would just fold most of his range and raise with hands that connect with the board.