There is a lot of shoving towards the end of an SNG, this is one of the big differences from cash.
At 12bb those charts are going to be based on the nash equilibrium. The equilibrium is manifested as the pushing and calling range for a given situation whereby neither side can improve and thus both will be break even over a large enough sample. This is an unexploitable range, note unexploitable is different from optimal.
For example on the bubble, if I'm shoving on another stack somewhat smaller than me.. the nash pushing range may be 70% and the nash calling range may be 15%. If I shove 70% and he calls 15% neither of us are exploitable and we'd be break even over a large enough sample. If I shove 70% but my opponent calls only 5% we start to make money (as he deviates from nash).
We could stick to shoving 70% but the exploitative response to him calling 5% would be to increase our range to shoving 100% (any two cards).
You say that sometimes you flip sometimes you don't.. you're forgetting all the times you pick up the blinds (worth more than 10% of your stack at 12bb) the % of the time your opponent folds and you pick up the blinds is your fold equity and this is built into the correct shoving ranges.
I understand this might be somewhat beyond the scope of the basic SNG strategy but in my opinion if you don't have a fundamental understanding of why you're shoving you will make mistakes in the long run.
I've added you on the community tool and am happy to answer any questions you have.