Synergy Bonuses + Tumble Skill AC Benefits

Extrapolating from values found in both the Player's Handbook and the Epic Level Handbook, the values below reflect the synergy bonus(es) a creature ought to receive for the number of skill ranks they possess in a skill that offers them.

5+ ranks in appropriate skill = +2 synergy bonus to appropriate skill check(s)
15+ ranks = +3 synergy bonus
25+ ranks = +4 synergy bonus
35+ ranks = +5 synergy bonus
45+ ranks = +6 synergy bonus
etc etc

In effect, for every 10 ranks possessed in a given skill beyond the first 5 ranks, any synergy bonus that skill offers improves by 1.

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As far as the dodge bonus to AC gained from Fighting Defensively or a Total Defense is concerned, possessing ranks in the Tumble skill should increase that bonus as follows:

< 5 ranks = +2 / +4 dodge bonus to AC ( fighting defensively / total defense )
5+ ranks = +3 / +6
10+ ranks = +3 / +7
15+ ranks = +4 / +8
20+ ranks = +4 / +9
25+ ranks = +5 / +10
30+ ranks = +5 / +11
35+ ranks = +6 / +12
40+ ranks = +6 / +13
45+ ranks = +7 / +14
etc etc

In effect, for every 5 ranks of Tumble gained beyond the first 5, the dodge bonus to AC gained from Fighting Defensively improves by 0.5 (rounded down).  The bonus gained from a Total Defense is always twice the value gained from Fighting Defensively.