the instructions i read are 200fcr, full tank, max leap, portal. someone later said that bportal involves leap + portal at the same time.
from a very long time ago, there was a flame bellow glitch - where leap would cause glitchy states. so i'd guess try casting portal before and immediately after. like the portal glitch llama posted, the portal is cast right at the landing location of a leap mid leap, which causes a stray 'entity' to wall block. i'd guess that the original theory that "enemies with no space would die" indicates that the leap and then immediate portals after leap created space that enemies would be displaced by and then die.
which personally, cannot make sense. there is already code to displace enemies, and even at the limits enemies don't die - druid boulder, for example, can push enemies infinitely without causing them to despawn - which is probably what led to a revision of what was actually happening.
if i had to guess, max leap was stated to keep enemies away. this means, imo, the leap needs to be small, maybe even on top of an existing portal, maybe followed by another portal. because lvl 1 leap already takes you across the screen. if the bportal could be activated across the screen where enemies are chasing, why max it? maxing it increases the radius at which enemies are knocked back, which to me implies a small leap where enemies can gather around and kill you or a long ramp up time where the character can't move and can only cast portals. bportal is likely a portal, then leap on to first portal while spamming another portal or two. if done quickly enough, the idea is that the new portal exists on top of the old one, which is where the 200 fcr causes the desync so the old one stays. my guess is the new portal has new code to handle this 'impossible' collision that shouldn't happen due to leap. that's also how i interpreted 'full tank'. i assume this barb goes full vitality to sustain being punched in the face while doing nothing but portals.
i may have details wrong, again, i'm just guessing from the clues people have left.
as a software enthusiast, i'd guess that the collision is 'impossible' - meaning this scenario falls through the 'if' statements that should have caught every normal scenario. it could be running code from the rest of the function if this function also handles something else? overflow to a corrupted function pointer because it doesn't return?
From:
https://forums.d2jsp.org/topic.php?t=108783808&f=148