Thrust and efficiency of Lorin Ramjet (Report by Sänger and Bredt) increase with the square of speed, with the square root of combustion temperature. Ramjet will start working around 300 km/ h, studies considered 300 m/ sec airspeed. Yield circa 12'000 HP per square meter of main bulkhead area. At higher altitudes, (calculations were made for a top speed of .9 Mach and 12 km ceiling, intended in a pursuit airplane, engineers thought Lorin Ramjet would not work above 18 km, because of poor combustion), thrust and propulsion power decrease, slightly less than density of air, but propulsion coefficient and efficiency increase because of lower temperature of fresh incoming air. At ground level and 300 m/ sec airspeed, thrust is 3'000 kg per square m of bulkhead area. Range increases from 367 km at ground level, in a case proposed in https://www.enginehistory.org/Rockets/LorinRamjet/LorinRamjet.shtml to 1'100 km at 18'000 m. Duration of flight for a given fuel load was maximum at 14'000 m height, decreased slightly above this, for a 6'000 kg total airplane weight, 1'000 kg payload, 2'400 kg of fuel, wing area 30 m2. Athodyd operating at higher temperatures losses efficiency, smaller athodyd impose higher working temperatures. Propulsion power increases with third power of speed.
They advised 2 m diameter Ramjets. Minimum speed at which diving is not needed to accelerate, at 12'000 m height, was 430 km/ h. Test of this tube on conventional airplanes were conducted at 100 m/ sec over a Do-17Z, then 200 m/ sec airspeed. For the design considered, speeds were 1'100 km/ h at ground level, and 950 km/ h in mid stratosphere.
I've suggested having a Pulse Jet inside the Ramjet, Athodyd tube diameter modified accordingly, pulsejets provide power at zero airspeed, and could carry Ramjet to its start speed. Intake duct angle was determined being best at 10º. Inside a duct, heat form outer parts of pulsejet would be added to thrust; if a double duct wall is installed, same would happen with heat of outer side of ramjet.