Using transform.position to modify speed of scrolling texture

Questions & Answers
1

I have a top down shooter where I want the position of the player to affect how fast the ground texture is scrolling on the object below them. While I could get it work while there is no player input, while the player is actively moving, the texture speeds up very fast (when going + Z) and goes backwards (when going - Z). I cannot figure out why it is doing this and what the workaround is

using UnityEngine;
using System.Collections;

public class ScrollTexture : MonoBehaviour {

	public float scrollSpeed=.01f;
	public GameObject modifier; 
	public Renderer rend;
 
	private float modifiedSpeed;
		
	// Update is called once per frame
	void FixedUpdate () {

		modifier = GameObject.FindGameObjectWithTag("Player");
		modifiedSpeed = ((modifier.transform.position.z + 6.0f) / 50.0f);

		float speed = scrollSpeed + modifiedSpeed;

		float offset = Time.time * speed;

			rend.material.SetTextureOffset ("_MainTex", new Vector2 (0, offset));	
	}
}
2

I decided to go a different route and use an if statement to control the speed

		modifiedSpeed = (movement/1000)*((modifier.transform.position.z + modifier.GetComponent<PlayerControllerAir>().zMax)+1);  //creates speed modifier based on player z position

		if (speed < 1)
			speed= speed+modifiedSpeed;
		if (speed >= 1)
			speed = 0;

		rend.material.mainTextureOffset = new Vector2 (0, speed);