1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

from collections import deque
from math import ceil, sqrt
import sys

# input = sys.stdin.buffer.readline
# def print(val):
# 	sys.stdout.write(str(val) + '\n')
for _ in range(int(input())) :
	n = int(input())
	a = [int(i) for i in input().split()]
	mx = max(a)
	ans = -1
	for i in range(0, n-1):
		if a[i]>a[i+1] and a[i]==mx:
			ans = i+1
	for i in range(1, n):
		if a[i]>a[i-1] and a[i]==mx:
			ans = i+1
	print(ans)