That may seem logical, but the answer is NO, you do not increase the amount of NPK in the mix, and you should still use 16 ounces per 30′ Soil-Bed.
The Mittleider Magic Weekly Feed sold in stores is 13-8-13, and 10-10-10 will work okay as a substitute. So, I do not recommend you change the amounts used, nor the application rate. However, if there is any indication that your plants’ growth is slowing down, just give an extra feeding in the middle of the week one time, and maybe a second time later for tomatoes & melons.
Plants don’t need large quantities of fertilizer at one time, but rather they need a little bit all the time. One of the “Organic” enthusiasts’ complaints with growing with “chemicals” is that they
are over-used (and sometimes they are!), and since organic growers use manure and/or compost with .5 – 1.5% NPK, you can see where they are coming from.
However, in order to get decent results from manure and compost, they must use large quantities. So, if they put as little as 5% by weight of manure/compost into a 30′ Soil-Bed, they will have used 150-200# of manure/compost, and yet will only have applied 1-3# of actual NPK.
By applying just 16 ounces (1#) of Weekly Feed to that 30′ Soil-Bed, and doing it weekly as needed, you will expend far less time, effort, and cost, and your plants will receive just what they need – not only of NPK, but also the other 10 nutrient compounds that are essential for healthy plant growth.