Random signal lost or extreme weak signal with remote controller on ISM frequency (433Mhz)
How much is 30% more dB?

Ricean fading or (reflection cancellation) will be your dominant cause of dropout even if RSSI or SNR shows adequate but marginal signal, so reflective surfaces and people interfering with reflections can cause dropouts when a reflected signal is near equal amplitude but out of phase with the main signal path.  

Keeping the whip antenna at right angles to the direction of propagation give the most signals.  To see if you are in a Ricean Fading zone with weak signals, behind the Tx, move the unit on a table top slightly over a +/- 1/2 wavelength zone in small increments to FIND a dead spot and then you know you will get dropouts with random orientations at that distance or path loss.  Try to get the RSSI or AGC signal out of the Rx to display on a scope to get better sensitivity to Path loss, interference and Ricean Fading Effects.

Then consider the best gain/dispersion antenna and location for the fixed receiver with an improved ground plane for the antenna.