As a rule of thumb you should see about 15-20% of the weight on the tailwheel. If you find it varies much from that you may have a CG problem or have the main gear out of optimum position. Here is an example: my FMS P-51 with 3300 battery weighs 2605 grams and has 458 grams on the tailwheel. This is 17.5%. If I put in a much larger battery the CG would go forward and the weight on the tail would be less. Vice versa for a much smaller battery...the CG would be aft and the weight on the tail would increase.