Yes, you are right, the radius must be few kilometers. the main issue, is detect we have problem in base or rover side. Here appropriate to refer "divide and rule". It will be perfect to have "verified" base and rover, and provide test
1. Triumph-1M base with "verified" rover
2. "Verified" base with Triumph-3 rover
You can provide simple test for RSSI estimation at 100' (30.48 meter) with internal and external antenna. In base station set permissible output power(1, 4, 10 or 35W) and in receiver side record the RSSI values. The test results can help us understand and detect problem.