All British tubas up to the 19" era brought into serial production on the 3+1P compensating Eb and BBb tubas (marked Besson or Besson Imperial until the Sovereigns came up around 4 years later in 1982) had bells with very little flare. Some called that bore profile exponential.
The Indian 1000 series may have the same valve section wrap as the old student models made in the UK, but the bell shown has much more flare.
When I was the director of a very poor youth band we were happy to loan one of the tiny Eb Besson Westminster’s. It was considered hopelessly out of tune. I very soon found out that the design of the 3rd slide was not about having the correct length of tubing, but about making it possible to stuuf the instrument into a case. When we pulled that 3rd slide well beyond the safery provided by the main frame, it was as reasonable as may be expected from a 3 valve instrument.
Once and only once I saw that little Eb model for sale in a 3+1p non-compensating version. Regretably I didn’t buy it.
Klaus