Ok How the Sl order works.
First if you want to sell at 431, all u need to do is place a Normal order to sell @ 431.When the price reaches 431 it will be sold off. No need to give stop loss for that.
The stop loss order if u see will have a trigger price and a price. In case of sell orders, the price has to be lesser than or equal to the trigger price. What happens is if the price falls and reaches your trigger price, your order gets triggered and it will get executed at your price. Please note that if the price is 425 and u place a sl sell order with trigger at 431, it means the order has already trigered because the price is 425 ie below 431. So your order is activated and it will get executed.
So when do you use a Stop loss order to sell?
Suppose you bought 50 shares at 431. You want to take a risk of only 3 rs per share. ie if the price falls to 428 you want to square off. In that case 428 becomes your stop loss.
How u place that order?
You place an identical sell order, ie 50 shares with trigger at428. And you give the price at 427.9. Now what happens? As the price falls and reaches 428 your stop loss is trigerred and your order is now activated. As the price reaches 427.9, your order will be executed depending on how many orders were activated before your order. Now suppose your stop loss got trigered but the price fell quickly to 426. It is quite possible that your order does not get executed at all. Tht is because, as soon as the sl is trigered your order will show as sell 50 @ 427.9. But since the price fell too fast there may be no buyers ready to buy at that rate. And your order gets executed only if there are buyers to buy at the particular rate.
The second problem u mentioned might be similar one. By the time you placed the order the price would have already crossed 422 so it wont get executed at that price since for you to buy at 422 u need someone to sell at that rate. Which no body would be ready coz the price is above 422.
How to place a SL buy order?
Suppose you have shorted 50 shares at 431 and want to limit your losses at 3 per share, ie you want to square off or buy back if the price rises and crosses 434. Then you place an identical buy order with 50 shares and triger at 434 and price at 434.1. When the price rises and reaches 434 your order is activated and will get executed at 434.1 Similar to previous case if the price rises suddenly and shoots up to above 434.1, very much possible your order does not get executed.
In such cases if you leave the price column blank, then your order will be executed at the market price as soon as the sl is trigerred.
Hope it helps