I appreciate that I am perhaps not the best person to be giving any advice on card sleights, but with this one I always start by sliding the bottom card over just a fraction before I start spreading. It may not be the most elegant way, but it does work for me.
Assuming you are right handed.
1. Hold the deck in left hand dealing postion.
2. Grip from above with the right hand as if you were squaring the deck up at the same time...
3. Use the index finger of the left hand to slide the bottom card to the right a few millimeters (even up to half a centimetre). It really doesn't have to be slid far, but this initial kick off helps me trmendously. I have the cards tilted slightly downwards at that moment and besides it is covered with the right hand.
4. Now the cards can be spread as normal, as explained in previous messges using th eleft thumb to kick cards ver into the right hand spread.
5. When the time comes it is now relatively easy for the left hand index finger to push the bottom card as far over as necessary before being collected by the right hand fingers.
This may not be the "official" method, but it works for me, and we are after all meant to adapt to own own. If you are still having problems at step three you could always kick the bottom card over a bit further, but I suspect you will be alright.
if this didnt help, I apologise for confusing even more
