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

_39 = '1445b'
# a1 = []
# n = int(input())
# for i in range(n):
#     a,b,c,d = map(int, input().split())
#     a1.append(max(a+b,c+d))
# for i in a1:
#     print(i)
_40 = '1445a'
# t = int(input())
# flag = False
# k = []
# count = 0
# r = 0
# for i in range(t):
#     if i != t and i != 0:
#         l = input()
#     n,x = map(int, input().split())
#     a = list(map(int, input().split()))
#     b = list(map(int, input().split()))
#     b.sort(reverse = True)
#     for i in range(n):
#         if a[i] + b[i] <= x:
#             count += 1
#     if count == n:
#         k.append('Yes')
#     else:
#         k.append('No')
#     count = 0
# for i in k:
#     print(i)
_41 = '1437a'
# k = []
# for i in range(int(input())):
#     l,r = map(int, input().split())
#     if 2*l > r:
#         k.append("YES")
#     else:
#         k.append("NO")
# for i in k:
#     print(i)
_42 = '1433c'
for i in range(int(input())):
    n = int(input())
    x = list(map(int,input().split()))
    m = max(x)
    ind = -1
    for i in range(len(x)):
        if x[i] == m and ((i>0 and x[i] > x[i-1]) or (i<n-1 and x[i] > x[i+1])):
            ind = i +1
    print(ind)
