Dear Mr. Azher

The burner is usually set small angle to the kiln axis and slightly directed  to material . Yet it must be considered that the material is being cooled   by the steam of secondary air flowing over it . providing that may not overheating showing up  in the material if the its thermodynamically  favourable to let flame sweep over it , to prevent the material getting too hot into the cooler the last section of kiln outlet is used as cooling zone

the tip of burner pipe than stands normally in the kiln at distance from 0.5  to 1 m .

Good result are also obtained with the drawn burner ( 0 m ) and fit it with longer flame ,

And you should  observe your kiln shell temp . aerodynamics in the kiln hood. meant the parameters  of airs primary , secondary , thrust , etc

Of Course there are so many of further imposures like

Dust content , first parts of cooler , coating size , lining condition , secondary air temp, swiral air direction of rotating , atomizing and oil preheating  (if oil burner ) ,kiln filling degree , and safy magren of fuel theoritical and actuall

With that`s shares by assistance with friends you could use it well

Have a nice day

ILA