It's a back and forth OB.
UC has inherent Evasion which relies on a certain amount of Dexterity to function properly.
3) UC's Inherent Evasion. A portion of the Unarmed Combat level trained acts as though it were Evasion levels -this amount changes between Ranged and Melee rounds, and is affected by the Combat Gi. This portion is supposed to be pre-item-bonus , so that UC-boosting equipment, save the Gi, doesn't affect the inherent Evasion level. 'However, testing has suggested that the evasion level is, in fact, affected by any UC boosting items. ' Without the Combat Gi, 1/3 of the trained UC level acts as though it is Evasion. With the Combat Gi, this increases to 50% of the trained UC level during Melee. UC Evasion functions as normal Evasion (described below), and should be similarly affected by ranged bonuses, Dexterity matching, and stacking with Displacement Boots and the Rune of Balrog Flame.
Evasion no longer grants any defensive Dexterity as of 3rd of September 2008 Evasion greater than your Dexterity is only 60% as effective. This means that you have a choice of training only evasion to counter only enemy weapon "+" to-hit enchantment, or more dexterity than evasion in order to counter both enemy weapon base to hit and DX-based cth. Note: Only trained Evasion is 60% as effective. Evasion granted by Displacement Boots or another source give full effect and are stacked AFTER the penalty has taken place.
Normally as long as you have more than half of their Dex they will not get double hits as long as your Dex is unopposed and you will also get a hit. To-Hit will determine this though.
To-Hit makes the difference here as well as your strat.
All in all you will need a scientific calculator to determine just how much it will help you against certain opponents or trust the Guides given and use a simple calculator.