First, comments on activity in your area. The OBENCO horizontal Rodessa activity is at least 10 miles away to the ESE / plus your area is structurally low to where they are drilling (and their results have indicated low = wet wells). You are north of the old Rodessa oil field that is pretty much played out right now. BRG (which may be the mother company of BROGO) has permitted a recompletion on an inactive well about two miles to the north along Turkey Creek.
Basically - things very quiet in your area and you are not in any active trends right now.
Don't know anything about other leasing in your area. But the 1/5 royalty is on the low side IMO - should ask for 25% or at least 22.5%. The money to be made here is in production so the higher the royalty the better. However, if you either need more money up now and/or believe that there won't be much drilling, push for the higher bonus and keep the 20% royalty.
Does your comment on post production costs mean that they are not offering a "no cost" lease? Keep in mind that being on the hook for various production costs can cut your royalty payments by 10 to 20% over the life of any producing well you may end up being part of.
Your block size (assuming you own 100% of the minerals) is a good sized block - this gives you some leverage in negotiations.
Good luck on this effort!