I’m betting the 0.042 is actually 1/24th or 0.041666667. What it means is that their combined 1/4 interest in 160 acres would have been 40 NMA. The other inheritors have each gotten pieces, so assuming there were 5 others, including you and they were all equal shares, each would have 1/4 divided by 6, or 1/24 in the 160 acres. 1/24 x 160 acres = 6.66667 net mineral acres out of the total 160. The tracts might be split by the Counties based on abstract numbers and that’s where you’d get the 3.333 nma. All of these are subject to rounding. The person they sold the land and 75% of the minerals to probably have the executory rights, and negotiated a 3/16 royalty rate and it’s apparently producing. With no production, you’d receive nothing but you’d still own the NPRI of 1/24th, and wait for the next lease to be negotiated. Newer leases will have a 25% royalty, so as I showed in my first answer, you would have a net revenue or net royalty interest percent of 0.0104…
I’m in Austin, too, so if you have more questions, I’d be happy to help. We are all in this together with sharp elbowed operators. 