The scale of the sight is off in relation to the weapon. It's so large it actually looks more like a special unit made for the M2 .50 BMG then the normal rifle version.
P90 Tri-rails are a bit unusual since the vast majority of military units produced have one of the factory FN sights.
Semi-auto PS90s in Tri-rail are fairly popular though.
You are right about the P90 but about the EOTech, the most fitting EOTech sight for P90 is the EOT551, the second largest EOT, it has the illumination like ACOG 6X18 and has a larger view compared to standard FN sights, standard FN sights are the worst sight i've ever tried on a weapon, it's too low and it hurts my cheek when aiming it down, and the tritium just sucks, i can't see it clearly at day. so i told my chief officer about this (i'm from SWAT, this P90s are given to point-man) and i got the TR version, and as i know, M2 can't fit any optic even if you give it a Rail
I know normally people put a EOT555 on it, but it wouldn't look that huge on the P90. I've seen and handled several, and the scale is off. I wasn't saying it WAS a M2, just that no other EOTech would look that giganto on a P90. The tritium isn't the problem with the sight in the day, it's the horrible light collector and fiber optics. There is an aftermarket kit that uses an adjustable LED to light the sight up better making it far more usable.
I have PS90 with an 2x20 ACOG TA47-2 on a TROS mount. Trijicon really knows how to make stuff work, but it's clear the P90 wouldn't ever be bought any military if had a nearly $1000 higher cost because of coming standard with a first class optic.
http://fnforum.net/ will have everything anyone would ever want to know about P90s
