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

import sys
import math
from collections import defaultdict,Counter

input=sys.stdin.readline
def print(x):
    sys.stdout.write(str(x)+"\n")

# sys.stdout=open("CP1/output.txt",'w')
# sys.stdin=open("CP1/input.txt",'r')

# mod=pow(10,9)+7
t=int(input())
for i in range(t):
	n=int(input())
	a=list(map(int,input().split()))
	ma=max(a)
	for j in range(n):
		if a[j]==ma:
			if j==0:
				if a[j+1]<a[j]:
					print(j+1)
					break
			elif j==n-1:
				if a[j-1]<a[j]:
					print(j+1)
					break
			else:
				if a[j-1]<a[j] or a[j+1]<a[j]:
					print(j+1)
					break
	else:
		print(-1)
