The ratio works as follows:

If your level is less than (tlevel - 8), you earn less than normal guild experience, based on the difference between your current level, the minimum level for you to make full tech, and the penalty attached to your guild level bracket.

If the difference between your guild level and your player level is above the benchmark for your guild level bracket, you will earn progressively more tech as a result.

For example, if your guild level is 15, you will earn extra guild experience for being at least level 20 - above 15 + 4.

     Guild Level     Benchmark    Penalty
      1 - 20            4              -
     21 - 30            8              1
     31 - 40           10              2
     41 - 50           ??              3
     51 - 60           ??              4
     61 - 70           ??              5
     71 - 80           ??              6

In short, -8 ⇐ (mlevel - tlevel) ⇐ benchmark → 100% gexp.

TLDR: If your guild level (tlevel aka tech level) is higher than your character level, you get less guild (tlevel) xp.