Recently I modified several cheap instant start electronic ballasts for small lamps and tries to make them preheat 2ft T8 tubes, which included 1kohm PTC resistor, regular starter and a bit of both. I got the best result combining both of them as on PTC alone the ends glow blue when starting, indicating cold cathode, same goes for the starter but it is more faint, when combining both together I get the longest preheat and no blue glow is visible on cold start, does that mean it is preheated sufficiently? Because in preheat start CFL and magnetic gear the ends usually glow red, however the contraption I made do not exhibit this behaviour.

  Instead of going though all that trouble have u  thought of  using a push button switch to manually preheat the tube.  All u need to do is hold switch close for 2 or 3 seconds and release.

I can do that and I tried it, it still doesn't preheat properly with it shorted, must've been the feedback transformer then, have to halve the primary turns.

At least visible dim orange glow means preheat is OK. When the discharge starts between filament turns, preheat is enough, or more than enough. Look at IEC 60081 to be sure, it defines preheat current for HF in rather complex time dependent way. Though, a proper means to verify this (a properly calibrated HF current probe) is $200+ even in cheap Chinese versions, like Micsig ones.

Here is a screenshot from Russian version of IEC60081 regarding 18W 600mm T8 tubes:

At least visible dim orange glow means preheat is OK. When the discharge starts between filament turns, preheat is enough, or more than enough. 

After reducing the number of primary turns to just 1, I installed a switch just like funkybulb suggested and I can see a dim glow, before there is nothing, now I just need a circuit that does this automatically. Unfortunately I don't have the gear to measure preheat current, but from mains side it draws 60mA when preheating, and at full intensity, a perfectly normal 80mA. Cheers for the help!

Some literature states that correctly preheated cathode (at the point of the ignition attempt) shall have resistance 4x higher than cold, it is just another way of saying the temperature has to reach ~950K.
This could be a good criteria for evaluating an existing ballast (monitoring voltages and current using a storage oscilloscope and then extract the real resistive component and how it evolved over time during the preheat phase by processing the data), but quite impractical one to implement within the ballast alone (as a preheat control method). Plus it checks only how the preheating matches the particular lamp piece, won't tell how it would behave over the spread of lamp parameters.