Hi Leo, welcome aboard.
I'm not familiar with the F70 and F100, but a look at basic performance principals should give you the answers you're looking for.
I think the 'key' to the answer lies within your own statement that the V1 / Vr increase is required for Normal, as well as for Flex operations.
It would appear, on the surface' that your engines are Flat Rated up to 30°C, and decline in thrust thereafter.
In using the Flex Temp technique, basically you're reducing the engine thrust to the point where, at that assumed temperature, the aircraft would be performance limited at the given weight. Therefore, any further performance discussion will be identical for both a high temperature day with the aircraft at limit weight, and a Flex situation where you've artificially put the aircraft in a performance limited situation.
From your remarks, I assume that for your aircraft, and for a given weight, the V1 / Vr / V2 relationship is the same up to 30°. Above 30° where thrust is declining (or you're flexing), V2 must stay the same as it is a minimum speed (unless you're using an increased speeds schedule where V2 > 1.2 x Vs).
The problem now lies in the acceleration from V1 to Vr at lower thrust, and the acceleration from Vr to V2 within the Takeoff Distance Available (TODA), also at lower thrust. If these two acceleration distances are excessive, one solution is to increase the V1 and Vr, bringing them closer to V2, thus decreasing the overall acceleration distance from V1 to Vr to V2, and containing it within the TODA. This works well from the performance perspective, provided that the increased V1 does not encounter Accelerate-Stop limits within the ASDA. For 2 engined aircraft (e.g. F70 and F100), the requirement to accelerate from V1 / Vr to V2 is usually a tougher one to meet than the accelerate-stop case.