sit on butts or tailbone in V-Ups?

Hi.

I want to know when doing V-Ups, where should I sit on, my butt or tailbone?

I asked similar questions on Straddle Ups, MN/PE2

and Jon Douglas gave me good advice to sit on butt.

(https://www.gymnasticbodies.com/forum/topic/19858-mnpe2-im-straddle-up/)

I assume this advice is same for PE3, but when I did it, it was hard.

and sitting on tailbone showed much better ROM and felt ... natural. 

so I'm confused. Please give me some advice. 

If you did both and found the wrong one 'natural' that's a flag to me. I'd want to see an actual video of you doing it to see if we are all talking the same language.

Cole Dano said:

If you did both and found the wrong one 'natural' that's a flag to me. I'd want to see an actual video of you doing it to see if we are all talking the same language.

https://youtu.be/FVtua__cTvU

Here is the video.

on first round, I tried to sit on the butt and I think it is really hard to contract my abs because I can't lift my legs high enough with butt-sitting.

on second round, I tried to sit on the tailbone, showing better control and contraction on abs. 

How do you think? 

Second round looks much better. At first round you were unable to complete a single rep.

It was a language problem, 2nd round is how you need to work. You can check back in as they get solid.

Cole Dano said:

It was a language problem, 2nd round is how you need to work. You can check back in as they get solid.

Do you mean I have to curve my back more rather than stiff and straight?

I mean do them like your second example and get stronger at them. When they get stronger put up another video for more feedback.