From what I can tell, from standard OSI/EA Ultima Online standards, item enhancing has a chance to change/improve the values of: resistances, durability, luck, or the requirements to wear certain armor. If you are enhancing a weapon there is the chance to change/improve the values of: damage type, durability, luck, or the requirements to wield the weapon being enhanced.
That is, unless staff has amended/customized this ruleset, the out come you are looking for is not found through item enhancement.
Also...
A crafted items potential for minimum/maximum properties is of course determined by the type of runic hammer a crafter is using. OSI/EA only has 7 types, but of course we have 13 types on Evolution. That said, I am unsure how many properties a platinum hammer grants as a minimum/maximum, but keep in mind a weapon has a pool of 24 potential properties to be crafted with. For a Valorite runic hammer back in the day, 5 was both minimum and maximum.
Conclusion...
I believe you might be having a bit of bad luck in crafting a weapon with two hit (magery) spell's attached. Even if 10 was the minimum/maximum for a platinum runic hammer; that would still leave 14 other options, left out, for each weapon you crafted. Even less when you are using a lesser runic hammer.
I hope this helps you out Swine, and keep in mind, I am certainly not 100% on anything I mentioned here: since Evo-Staff has the option to change the default settings as they see fit.
--Sturger--