Here is a bit different approach to calculating position size. Below method is applicable for Holding stocks and not for intraday. Will try to substantiate intraday at the end.
Equal risk-weighted method:
What we try to do here is allocate the amount based on the stock volatility. Higher the volatility lower the allocation and lower the volatility higher the allocation. The idea is each stock in a portfolio should have the same impact on the portfolio P&L.
No. of shares = Portfolio Amount * Risk factor / Volatility
Risk Factor = % basis point impact on a portfolio. Say, each stock should have a 10 basis point impact on the portfolio. Which give the risk factor of 0.001 or 0.1%
Volatility = One can either use standard deviation or ATR to get the volatility of the stock.
Here is the allocation for reliance and idea would come up if you had 100,000 as capital and 0.2% risk factor.
Reliance is quite stable compared to Idea and hence higher allocation.
You can check this link to get position size on the above method - Inuvest.
For intraday, you can multiply the above to the leverage you would like to use.
Alternatively, since the margin offered by brokers takes into account the volatility you can use that to get an allocation. Say your capital is Rs.100,000 and want to have 10 stocks in the portfolio, hence you would allocate max of Rs.10,000 to each.
No. of shares = 10000/margin amount of stock.
Margin offered on Reliance is 10X and no margin on Idea. Hence, the total exposure in reliance would be 98,314 while in idea it would be 9,998 only.
Hope you are able to get a different perspective.