Thanks for the clarification. Another question. Do these play a role something akin to inlet ramps during high AoA? The Sukhoi aircraft do have insane AoA!
Not exactly certain what you mean there. The F-15's and F-14's movable inlet ramps are to slow down supersonic air. Any air flow over them of course will influence the aerodynamics at that time but the FLCS stability augmentation system would deal with that. Angle of attack is created by rear stab deflections, but the higher the AoA, the less lift available for the airfoil, and that include the lifting body as well.
Prior to computerized stability augmentation system, a pilot would have to learn his aircraft's idiosyncrasies manually, if he pulls back on the stick, it is up to him to know his aircraft's pitch limit lest he stall his wings. And if he does stall, it is up to him to know how to recover. There were no AoA probes back then. But with 'angle of attack probes' (keywords image search) we can program the FLCS computer to limit rear stab deflections
REGARDLESS of pilot inputs. This is a huge misconception regarding Western fighters where some believe Western fighter designs cannot handle high AoA. These AoA limits are balanced between speed, altitude, pilot input and external loads. The calculations are transparent and designed to avoid pilot induced stall situations. For the Soviet/Russian fighters, those high AoA require exceptional airmanship to handle and recover. They may be available but based upon our investigations and conversations of Soviet trained Eastern European pilots, the airshow high AoA situations are to be avoided. Talk to any pilot and you will find the truth, that none like to approach his aircraft's AoA limits and if the aircraft is designed to prevent him from doing it to himself -- great.
Take a look at the PAK-FA's outline superimposed over the F-22.
I highly suspect the PAK-FA's wide engine spacing, to accommodate 3D thrust vectoring, necessitated the movable leading edge root extension (LERX). The PAK-FA's wing sweep is almost the same as the F-22's. The F-22's wing leading edges has continuous 'slats', which are the front version of trailing edge 'flaps', to increase surface area for lift. The PAK-FA's wing leading edges also does have 'slats' but the designers seem to need more, hence the movable LERX. The wings themselves are comparable to the F-22's wings in terms of surface area:
Sukhoi PAK FA - Wikipedia, the free encyclopedia
Wing area: 78.8 m2 (848.1 ft2)
Aerospaceweb.org | Aircraft Museum - F-22 Raptor
Wing Area 838 ft² (78.0 m²)
Not that much different for a clearly larger aircraft -- fuselage-wise. So it looks to me that RCS requirements forced those wing surface area and the desire to match the F-22 maneuverability -- movable LERX -- which remains to be seen if they are detrimental to the low RCS requirements. But then again, it could be argued that because of the movable LERX, the PAK-FA is not in the same RCS class as the F-22 or F-35. Way too early to tell.