i saw it but any tips and tricks still??? thanks

I apologize for not reading you carefully enough at first! There should always be some bend in the rider's elbows. This is for the comfort of the horse, for the safety of the horse, and for the safety of the rider.
What really helped me was, when I do the two-point position, putting my hands near the top of the horse's shoulders a few inches below the top of the withers (keeping a straight line between my elbow and the horse's mouth) instead of on top of the crest or holding onto the mane. I needed outside eyes (my wonderful riding teacher) to make sure I kept the straight line from my ELBOW TO THE BIT until I got the true feel of it.
I also HAVE TO concentrate each time I post to open my elbow when I rise and close it when I sit down. A lot of people have trouble doing this, and if they do not open and close their elbow joints their hands do not stay in the same place in relation to the horse's mouth irritating the horse and messing up contact. Of course I am always opening and closing my elbows at the walk and canter/gallop as the horse's head moves more at these gaits.
In your original post you said a straight line from the hands to the shoulders, as far as I am aware since Caprilli introduced the modern jumping seat the ONLY time there is a straight line from the rider's hand to the shoulder is when a horse is REACHING and STRETCHING his neck over a huge, wide fence or when the horse meets the fence wrong and has to make a supreme effort, reaching out forward as far as possible with its nose and neck, or when the rider meets the fence wrong, is left behind the motion of the horse, and gives all the rein he/she can so the horse has a chance to get over the jump without getting punished by the bit hitting his mouth (but hitting the horse on the back by falling back while the horse is in the air over the jump.)
Except in the above emergencies over the jumps there should always be some bend to the elbow (say 120 degrees to 90 degrees) so in an emergency you can give the horse more room to move his head and neck while keeping control. If the arms are completely straight going over the jump there is no extra reserve room for the horse's head and neck, which means that there is absolutely no margin of safety except for dropping the reins completely.
I apologize for not reading you carefully enough at first! At no time over a jump (except for emergencies) should the rider's arm be completely straight from hand to shoulder, there should (outside of emergencies) ALWAYS be a bend in the rider's elbow, the hands should follow the horse's mouth which means that the rider's elbows should close some (take off), open (during the flight over the jump), and close again during normal landings if you are keeping constant contact with the horse's mouth.
I am rather "old fashioned" about this. If you never have a bend in your elbow you will be accidentally abusing your horse's mouth pretty severely AND it will affect your own balance and position badly, usually leading the rider to topple forward and put all their weight on the horse's forehand at just the wrong time in the horse's stride or jump or landing, possibly leading to falls of both horse and rider.
If you are doing the old fashioned English hunt seat/modern 3-Day cross country seat I am afraid that the riders, leaning way back at the landing, have to straighten their arms AND hold the reins near to the buckle. This means that on landing and the first stride or so that the rider has NO control and cannot help the horse. They would do better to learn to keep contact over the jump, then the rider has control over the horse every second of the ride. This requires bends in the elbow!!!!!