so here is my little experiment. i did it for myself, but may be somebody else would be interested.
i
tried to match:
- the size of "NECA" writings on the back wall
- the size of those metal rods with holes
- the thickness of a glass shelf
and then i put the back edge of a glass shelf they all stand on on one level to imitate their standing on one surface.
i tried to catch some 1/10 figures with Freddy as well, because they will be the only help for me - i don't have any 1/4 figures.
i did it urgently on a low-level computer, measuring letters mainly with a naked eye, so there might be a mistake there. may be somebody can repeat that in some nice graphics program and with precise measurements, but the idea is: once you match the letters "NECA" on two photos, you have a simulation of two figures on one shelf in one scale.
now i think Deadpool's letters "NECA" are too small, making him too small also.
===========
so i'd say (or should i say "i hope") turtles are like Penguin in his hat, which would be like 1/4 human shoulder height.
there is also a way to measure in "NECA"s directly
like "an alien is 4 Necas high, a turtle is 3 Necas".