Spawn Time (EveryXsec) and Bullet Speed Ratio for Space Shooter

This question is kind of theoretical. I cannot really find the most appropriate ratio for a space shooter. Explained below:

What is the best ratio between

spawn enemies: EveryXseconds

and the bullet speed they have?

What am looking for is the best relationship between the two that is the time of spawning and the speed.

Say I start with the speed of 50 in which enemies are falling down. How often should be the enemy spawned to make it engaging?

BTW, what speed would you consider as a baseline for this kind of game?

Then every 10 points I increment the speed by adding 25 and I recon i should do something with the spawnTime (EveryXSeconds).

Thus what should be the baseline for the seconds of spawning the enemies and their bullet speed? What ratio should I maintain between the two to make the game run well while incrementing the speed of enemies?

There is no 'baseline' and no right and wrong. You have to decide for yourself how easy or difficult your game should be. What do you want to create for a gaming experience? Maybe you also let the player choose the level of difficulty. Create global variables for the Bullet Speed and your 'Every X seconds' conditions. The higher the difficulty level, the more enemies spawn and they shoot faster. You will not get around testing some values until you get a satisfactory result.

If the Enemies have different weapons with different bullet speed, your global variable "EnemyBulletSpeed" could be for example 1 for medium difficulty, 0.75 for easy and 1.25 for hard. Then set the speed of the bullet on creation to > object.bullet.speed * EnemyBulletSpeed <

Ps: I am sorry if it is a completely dumb question but what is the value of bullet speed in construct 2/3? I am asking out of curiousity. Is it pixel divided by time in miliseconds?

The 'Speed' property of the Bullet behavior describes the bullet's initial speed, in pixels per second.

Thanks for the reply @kriand . I still welcome contributions of other programmers may they be any.